Short Pulse Laser Absorption and Energy Partition at Relativistic Laser Intensities

Abstract

We have performed experiments at the COMET and Calisto short pulse laser facilities to make the first comprehensive measurements of the laser absorption and energy partition in solid targets heated with an ultrashort laser pulse focused to relativistic laser intensities (>10 17 W/cm 2 ). The measurements show an exceedingly high absorption for P polarized laser-target interactions above 10 19 W/cm 2 . Additionally, the hot electron population is observed to markedly increase at the same intensity range. An investigation of the relaxation process was initiated using time-resolved K α spectroscopy. Measurements of the time-resolved K α radiation suggest a 10-20 ps relativistic electron relaxation time. However modeling difficulties of these data are apparent and a more detailed investigation on this subject matter is warranted.

Nonlinear increase of X-ray intensities from thin foils irradiated with a 200 TW femtosecond laser

“…The radiation power thus rapidly approaches the total laser pulse power as a 0 increases. The number of radiating electrons also increases with the laser intensity weakly depending on target conditions 45 . For PWL intensities above 10 22 W/cm 2 the radiation process begins to dominate over the electron dynamics, reaching the RDR plasma Zone, where the interaction occurs.…”